KR100195768B1 - Polymeric composition comprising transient foam control reagent - Google Patents

Abstract

A foamable composition comprising an alkenyl aromatic polymer, blowing agent and a transient foam control agent that is effective to reduce polymer melt viscosity in the melt phase but nonmiscible and nondetrimental to the polymer in the solid phase.

Description

Polymer Composition Including Temporary Foaming Control

The present invention relates to foamable polymer compositions and methods for their preparation, more particularly foamable alkenyl aromatic polymer compositions comprising a volatile blowing agent and a temporary foaming regulator.

Alkenyl aromatic polymer foams, such as polystyrene foams, have been found to have a wide variety of uses, including insulation, cushion packaging, and the manufacture of shaped articles such as cups, dishes, and the like. When used as an extruded plate insulation material, an unstable blowing agent is typically incorporated into the thermoplastic polymer and the resulting mixture is extruded into a low pressure compartment and then foamed. Conventional blowing agents include chlorofluorocarbons (CFCs) preferentially due to the ease of use of these materials and the provision of excellent foaming properties. However, due to the long-term environmental impact of CFC blowing agents, manufacturers reduce the amount of CFC blowing agent required to ensure that the foam has a certain density (typically, the foam uses a large amount of CFC blowing agent). We have sought ways to use other less effective blowing agents that do not cause damage. In order to achieve these intended purposes, it is desired to provide a molten polymer mixture with improved (reduced) viscosity and other properties to enable the use of small amounts of CFC blowing agents or other less effective blowing agents.

In the past, attempts have been made to use plasticizers and / or plasticizer blowing agents in polystyrene foams to assist melt foaming, especially where very low densities are required. These plasticizers have been found to adversely affect the final foam properties and in some cases lead to permanent softening of the foam,

In addition, attempts have been made to stabilize foam formation by crosslinking foams upon foaming. However, insufficient crosslinking does not provide the desired stabilization, and excessive crosslinking makes processing difficult, so the use of crosslinkers must be carefully controlled. Moreover, crosslinking of such foams makes it difficult to reprocess foam scrap.

Thus, attempts have been made in the art to develop methods for producing extruded alkenyl aromatic polymer blowing agents that can reduce or eliminate CFC blowing agents.

According to the present invention there is provided a foamable polymer composition comprising from about 0.05% to 15.0% by weight of a temporary foam control agent and at least 50% by weight of an alkenyl aromatic polymer with a blowing agent. Temporary foam control agents are miscible with the alkenyl aromatic polymer in the molten phase and act to reduce the viscosity of the polymer melt upon foaming, but are incompatible with the solid polymer and have little damage to its physical properties.

The effect of the transient foam control agent is to modify the melt flow properties of the expandable polymer composition, in particular the primary alkenyl aromatic polymer component of the composition, but does not inhibit the desirable physical properties, in particular the solid phase properties of the polymer composition. To achieve this goal, the temporary foam control agent is incompatible with the alkenyl aromatic polymer at temperatures below the glass transition temperature (Tg) of the polymer and is fully dispersed into a sufficiently small area that does not adversely affect the physical properties of the polymer product. It needs to be a solid that can be. Compositions in the solid phase can be described in particular as microdispersions of the transient foam control agents in alkenyl aromatic polymers. Typically, the mixture is homogeneous and the transient foaming modifiers do not damage enough to detect the physical properties of the polymer in the solid phase by forming discontinuous, uninterconnected regions with particle sizes of 0.1 to about 50 μm.

At temperatures above the minimum foaming temperature of the alkenyl aromatic polymers, the temporary foam control agents are miscible with the alkenyl aromatic polymers, preferably melt, and are effective in reducing the melt viscosity of the composition.

Very low density foams can be prepared according to the invention by melt processing a polymer composition comprising at least 50% by weight of an alkenyl aromatic polymer together with a volatile blowing agent and a temporary foaming regulator under pressure above ambient pressure to produce a fluid mixture. . When using alkenyl aromatic polymers, the preferred melt processing temperature range is 180 to 230 ° C. The mixture is then extruded through a die into a low pressure compartment where the blowing agent is activated to foam the composition into the foam structure. The foam can then be exposed to atmospheric steam or hot air at 80-115 ° C. to further foam even low density foams. After the initial expansion of the foam followed by aging, the sequence of exposing the mixture to low pressure and steam or hot air is preferred. However, this method can be carried out almost simultaneously through an on-line process to immediately expose the extruded foam to steam or hot air.

Additional components of the expandable polymer composition may include polymers such as polyarylethers (particularly polyphenylene oxides), polycarbonates, elastomers (particularly polybutadiene, EPDM or styrene / butadiene block copolymer rubbers), polyethylene and the like. The expandable polymer composition of the present invention preferably comprises at least 70% by weight of an alkenyl aromatic polymer resin. Preferably, the weight average molecular weight of this resin is 100,000 to 300,000. Such molecular weight can be measured, for example by gel permeation chromatography (GPC). The term alkenyl aromatic polymer resin refers to a solid polymer of at least one polymerizable alkenyl aromatic compound and, optionally, at least one copolymerizable monomer. The polymer or copolymer comprises at least 70% by weight of polymer units derived from at least one alkenyl aromatic monomer of the general formula in the polymerized state.

Wherein Ar is a benzene-based aromatic hydrocarbon radical or aromatic halohydrocarbon radical, and R is hydrogen, methyl group or ethyl group.

Examples of such alkenyl aromatic polymers include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, ar-ethylstyrene, ar-vinylxylene, ar-chlorostyrene, ar-bromostyrene , Solid homopolymers of vinyl toluene, or solid copolymers of one or more of these alkenyl aromatic compounds with other copolymerizable monomers, such as anhydrides of acrylonitrile, maleic or itaconic acid, acrylic acid or methacrylic acid, or rubber -Reinforced (synthetic or natural) styrene polymers and the like.

Blowing agents useful in practicing the present invention are well known and may include solids or liquids that decompose or volatilize into gaseous products at extrusion temperatures. Preferred types of blowing agents include halogenated hydrocarbon compounds of 1 to 8 carbon atoms (particularly chlorofluorocarbons), hydrocarbon compounds of 1 to 8 carbon atoms, low molecular weight alcohols, nitrogen, carbon dioxide, water and mixtures thereof.

When these compounds are used as blowing agents, it is possible to use 10 to 200 g, preferably 50 to 150 g of blowing agent per kg of the polymer composition. Particularly preferred blowing agents include 1-chloro-1,1-fluoroethane (CFC-142b), 1-chloro-1,2,2,2-tetrafluoroethane (HCFC-124), 1,1,1,2 Tetrafluoroethane (HCFC-134a), dichlorodifluoromethane (CFC-12), trichloromonofluoromethane (CFC-11), n-butane, iso-butane, n-pentane, isopentane, water , Carbon dioxide, ethyl chloride, nitrogen and mixtures thereof. Highly preferred blowing agents include mixtures of CO ₂ and CFC-14b in a weight ratio of 5/95 to 50/50. Generally, blowing agents, such as CFC-142b or mixtures thereof with carbon dioxide, are less effective at obtaining suitable foam properties, and their use is not performed as hard as chlorofluorocarbons such as CFC-12. Therefore, a functional system for producing suitable foams with CFC-142b blowing agents is highly desirable.

The temporary foam control agents used to practice the invention are preferably from 0.1 to 10% by weight of the composition, more preferably from 0.3 to 5.0% by weight and most preferably from 0.5 to 3.0% by weight.

Suitable temporary foam control agents are C _2-30 aliphatic and aromatic carboxylic acids or polycarboxylic acid compounds and ester derivatives thereof, C _2-30 aliphatic and aromatic carboxylic acid amides, C _2-30 aromatic or aliphatic sulfones and amide derivatives thereof, C _5-30 aliphatic And aromatic polyhydroxy compounds, C _2-30 aliphatic and aromatic carbamate and carbamate esters, inert substituted derivatives of the foregoing compounds, and mixtures thereof.

Specific examples of the above-mentioned temporary foaming regulators include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, methyl urea, benzene sulfonamide, cyanoacetamide, N, N'- Hexanemethylene bisacetamide, m-nitrobenzamide, mannitol, piperazine bis-alkylcarbamate, piperazinebis-hydroxyethyl carbamate and the like.

In a particularly preferred embodiment of the present invention, the transient foaming regulator is selected from C _4-10 aliphatic dicarboxylic acids and mixtures thereof. In particular, mixtures of the aforementioned C _4-10 aliphatic dicarboxylic acids having a melting point of 110 to 130 ° C. are highly preferred temporary foam control agents. For example, mixtures containing 5 mol% or more of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and / or sebacic acid are particularly preferred. Particularly preferred transient foam control agents include mixtures of adipic acid and sebacic acid, in particular mixtures in a weight ratio of 10/90 to 50/50. In the most preferred embodiment using the above-mentioned temporary foaming regulator mixture, the eutectic mixture is used in a weight ratio of 30/70, such as for a mixture of adipic acid / sebacic acid.

Temporary foam control agents can be easily blended with alkenyl aromatic polymers by dry blending, concentrate blending, or melt injection. Preferably, the temporary foam control agent is fed directly into the extruder and then melt treated with the alkenyl aromatic polymer resin, blowing agent and other additives without using any additional mixers.

Typically, finely divided solid materials such as talc, calcium silicate, barium stearate or zinc stearate, magnesium oxide and the like can advantageously be incorporated with the polymer gel prior to foaming. These finely divided materials can be used in amounts up to 5% by weight of the polymer to help control bubble size. In addition, fillers, pigments, lubricants, wetting agents, antioxidants, flame retardant additives and the like, which are well known in the art, may be incorporated as desired.

In order to more easily understand the present invention, the present invention is exemplified by reference to the following examples which illustrate but do not limit the scope of the present invention. Unless stated otherwise, parts and percentages are by weight.

Example 1

The instrument used in the examples is a 3.2 cm screw extruder with two additional mixing compartments and a cooling compartment at the end of a conventional continuous feed compartment, melt compartment and metering compartment. An opening for blowing the blowing agent is present on the barrel between the metering compartment and the mixing compartment. At the end of the cooling section, a die orifice having a rectangular opening is attached. The width of the opening (hereinafter referred to as die gap) is fixed at 6.35 mm, while the height is adjustable.

Granular polystyrene having a weight average molecular weight of about 200,000 is dry blended with an amount of a temporary foaming regulator. Magnesium oxide and magnesium stearate are respectively mixed with 0.05 pph, talcum about 0.2 pph pigment 0.03 pph and brominated flame retardant 2.0 pph polymer granules. The compound is fed into the extruder at a nearly uniform rate (about 4.54 kg (10 lb) / h). Various blowing agents are injected into the extruder in the amounts specified in Table 1. The temperature of the extrusion section is maintained at 182 ° C. in the feed section, 193 ° C. in the melting and metering section and 204 ° C. in the mixing section. The temperature of the cooling compartment is adjusted to cool the gel to a uniform temperature of about 125 ° C. In runs 1 to 4, blowing agents containing CO ₂ and CFC-142b (soft chlorofluorocarbons which do not cause environmental problems) are used. Foam production conditions are specified in Table 1. The physical properties of the resulting foams are listed in Table 2.

The results in Table 2 show that when using the instantaneous foam control agents of the present invention, suitable polymeric foams can be prepared according to the present invention while using blowing agents comprising soft CFCs such as CFC-142b and mixtures thereof with CO. The foam composition of Trial 1 has a reduced density without compromising other physical properties. The composition used in Run 4 used a reduced amount of blowing agent (1.48 mo1 / kg instead of 1.62, reduction rate 8.6%), but the physical properties of the resulting cured foam are still acceptable.

Claims (9)

C _2-30 aliphatic and aromatic carboxylic acids and polycarboxylic acids and esters and amide derivatives thereof; C _2-30 aromatic and aliphatic sulfones and amide derivatives thereof C _5-30 aliphatic and aromatic polyhydroxy compounds; C _2-30 aliphatic and aromatic carbamate and carbamate esters, derivatives wherein the compounds mentioned above are inactive-substituted; And mixtures thereof; temporary foaming that is mixed with the alkenyl aromatic polymer in the molten phase and acts to reduce the melt viscosity of the molten phase but is incompatible with the polymer in the solid phase and has little damage to the solid phase polymer. A foaming agent and a foaming polymer composition comprising at least 50% by weight of an alkenyl aromatic polymer, characterized in that it comprises 0.05 to 15% by weight of a modifier. The composition of claim 1 wherein the transient foaming modulators hardly damage the physical properties of the polymer in the solid phase. The composition of claim 1 wherein the temporary foam control agent is a mixture of C _4-10 aliphatic dicarboxylic acids. 4. The composition of claim 3, wherein the temporary foam control agent is a mixture of idipic acid and sebacic acid. 5. The composition of claim 4 wherein the temporary foam control agent is from 10 to 50 weight percent adipic acid and from 50 to 90 weight percent sebacic acid. 4. The composition of claim 3, wherein the transient foam control agent is a eutectic mixture of aliphatic dicarboxylic acids. The composition of claim 1 wherein the blowing agent is 1-chloro-1,1-difluoro ethyne. A process for producing a foam by extruding the composition according to claim 1. Foam produced by the process according to claim 8.